Beware: Its April Fools Day

April 1 is the only day of the year when deceit and pranks are not just tolerated, but encouraged. Interest in the "holiday" is palpable in the Yahoo! Search box. Web lookups for "best april fools day pranks," "how to trick a friend," and "funny april fools day tricks" are all making more noise than an overinflated whoopee cushion.

But if you ask us, the most interesting prank-related query is this: April Fools' Day history. Would-be Allen Funts clearly want to know why everybody is allowed to lie to each other on the first day of April. Here's the scoop...

There are several theories regarding the origin of April Fools' Day, and none of them are 100% definitive. However, one does stand above the rest: The Museum of Hoaxes explains that in 1564, King Charles IX of France passed a law that changed the beginning of the year from April 1 to January 1.

News of the change traveled slowly. Those who were either misinformed or slow to make the adjustments still celebrated the New Year on April 1. As a result, they were mocked and pranks were pulled.

The urban legend experts at Snopes.com note that several other theories are worth considering. Some believe that the day falls on April 1 because of the arrival of spring, when "nature 'fools' mankind with fickle weather." Another possibility: The holiday "is thought to commemorate the fruitless mission of the rook (the European crow), who was sent out in search of land from Noah's flood-encircled ark."

Regardless of the origin, people show no signs of giving up the tradition. The number of Web searches for "april fools day prank ideas" are scary high. Everyone (and especially parents) should be on the lookout. That "$1,000 cell phone bill" your daughter hands you might not be the real McCoy.

To help out the gullible and easily tricked, we rounded up some of the most popular prank ideas from Yahoo! Search. Also worth checking out: some of the best online pranks ever, from Christian Science Monitor (remember Facebook's "LivePoke" feature?). Keep your guard up, suckas...